Neufeld



J. NEUFELD April 28, 1953 SPECTROMETER 5 Sheets-Sheet 1 Filed May 5,1947 E ii on 00 a mm mm INVENTOR. 50mg;- W

April 28, 1953 J. NEUFELD 2,636,994

SPECTROMETER Filed May 5, 1947 5 Sheets-Sheet 2 LINEAR AMPLIFER 55 |5blb 7 ELECTRICAL TRANSDUCING CIRCUIT INVENTOR.

J. NEUFELD SPECTROMETER April 28, 1953 5 Sheets-Sheet 4 Filed May 5,1947 a u O I X L 0 INVENTOR.

J. N E U F EL D SPECTROMETER April 28, 1953 Filed May 5, 1947 5Sheets-Sheet 5 N VEOBFmZ OZuDOwmu zi &

W N/w Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE SPECTROMETERJacob Neufeld, Tulsa, Okla.

Application May 5, 1947, Serial N 0. 745,988

17 Claims.

This invention relates to a method and apparatus for spectrograp-hicanalysis of various radiations and deals particularly with spectographicanalysis or" nuclear radiations such as alpha rays, beta rays, and otherradiations.

Various objects and advantages of the present invention will be apparentfrom the description which follows when taken with the drawing in which:

Fig. 1 shows diagrammatically a general arrangement for performingnuclear spectrographic analysis in accordance with this invention, saidarrangement utilizing frequency meters.

Fig. 1a shows a modified portion of Fig. 1 comprising a crystal counter.

Fig. 1b shows a modification of Fig. 1 comprising a shallow parallelplate ionization chamber.

Fig. 2 gives diagrammatically the output of a radiation pulse detectorin which the axis of n abscissas represent the time of occurrence of thepulses and the ordinates represent their respective magnitudes.

Fig. 3 gives diagrammatically frequency amplitude spectrum obtained bymeans of the instrument of Fig. 1.

Fig. 4 shows another form of nuclear spectrometer in which frequencymeasuring circuits have been eliminated.

Figs. 5a, 5b represent diagrammatically the shapes of various impulsesutilized in the arrangement of Fig. 4.

Fig. 6 shows a modified embodiment of a nuclear spectrometer utilizing aderivation circuit.

Fig. 6a shows a saw-tooth wave form.

Fig. 7 shows a modified form of nuclear spectrometer adapted formeasurements of weak radiations.

Referring now more particularly to Fig. 1 numeral H designates a sourceof radiation, of particles such as for instance, alpha or betaparticles. These particles are received by a suitable detector 12positioned in the immediate proximity of said source. The outputterminals of the detector i2 are connected to an electrical.

28, cathode 29, and an ionizable gas under suitable pressure. A suitablevoltage is applied to th electrodes by means of a battery 30 therebycausing an ionization current to flow through the resistor M in serieswith the battery thereby creating across the terminals of the resistor31 a corresponding voltage. The detector I2 is of a pulse forming typeand can be either a pulse ionization chamber or a crystal counter. Thepulse ionization chamber has geometrical dimensions that are sufilcientto absorb completely within the gaseous medium all incoming beta oralpha particles. The ionization produced by each beta particle producesin the output circuit an impulse which is an unambiguous measure for theenergy of the corresponding particle.

The crystal counter illustrated schematically in Fig. 1a. consists of aplate 35 of silver-chloride, two metallic electrodes 36, 37 adjacent toboth sides of the silver-chloride plate, the whole assembly beingmaintained at liquid air temperature Within a suitable Dewar vessel 38,the low temperature being necessary in order to eliminate the ionicconductivity of the crystal. The remaining components of the nuclearspectrome ter such as the electrical transducer [6 connected to theoutput of the crystal counter, and the cathode ray tube I! connected tothe output of the transducer it are the same in Fig. 1 and Fig. 1a.

Further information about crystal counters can be found in The CrystalCounter. A New Instrument in Nuclear Physics by P. J. Van HeerdenAmsterdam, N. V. Noord-Hollandsche Unitgevers Maatschapij 1945.

The voltage impulses derived from the output of the detector I2 aresubstantially of the form designated by numerals 1 to 33 in Fig. 2. Theyoccur in succession one after another in coincidence with the particlestraversing the detector l2 and have magnitudes that respectivelyrepresent the energies of the corresponding particles.

The principle of the method consists in selecting a determined timeinterval and considering during said time interval only a portion ofimpulses derived from the output of th detector l2 and namely impulsesthat represent a narrow energy range of the incoming particles. Assumethat the magnitudes of impulses representing the selected energy rangeare comprised within limits a and a+Aa where Aa is a small value.Consequently, only those impulses in Fig. 2 that are larger in magnitudethan a value a and smaller than a value a-f-Aa. are located within theselected energy range. Let the number of impulses satisfying thiscondition be 12. From the inspection of Fig. 2, it is apparent that ifrt-=0, then only the impulses 9, 19, 20, 23 and 29 will be larger than:0 and smaller than Aa. The number of these impulses designated by no is5. If a assumes a value m then only the impulses 3, 6, 13, 16, 1'7, and24 will be larger than 111 and smaller than Aa+d1. The number of theseimpulses designated by m is 6. If :2 assumes a value m then only theimpulses 26, 30, 31, and 33 are larger than on and smaller than Aaz.Consequently, the corresponding number 122:4. If a assumes a value asthen only the impulses 14, Y

25, and 27 are larger than (13 and smaller than Ads. Then the number ofthese impulses designated by m is 3.

The above illustration is based upon the assumption that the totalnumber of impulses during the interval of a single measurement of thevalue 11. is 33. In actual practice, however, the number of impulses isconsiderably larger so that in the measurement of various values of nsuch as no, n1, n2, n3, etc. the error due to statistical fluctuationscan be neglected.

It is apparent from the above that if a is allowed to vary continuouslyso as to cover continuously all the values from 0 to as and if,furthermore, the value A01. is maintained constant, then we obtain acontinuous range of corresponding values or n. If we plot all the valuesof a along the axis of abscissas and the corresponding value of 11,along the axis of ordinates we obtain a diagrammatic representationsimilar to the one of Fig. 3. It is apparent that each abscissa valuerepresents the magnitude of energy a within a range of width Aa.Consequently, the abscissas are measured in units of energy such aselectron volts, frequencies, wave lengths, etc. 0n the other hand, eachvalue 01: the ordinate represents the number of impulses per unit oftime, said impulses being within the energy range a, a-l-Aa.Consequently, the diagram of Fig. 3 represents schematically the energydistribution of impulses represented in their time succession by Fig. 2.

In order to obtain the intensity as corresponding to any single energycomponent a (i. e. defining a band limited by the value a and a-l-Aa)the following instrumental steps are necessary:

(1) Apply the output of the detector l2 to a channel A that willtransmit only those impulses that are larger than lZ-I-Ad and determinethe number N1 of impulses thus transmitted per unit of time.

(2) Simultaneously with the step (1) apply the output of the detector l2to a channel B that will transmit only those impulses that are largerthan a and determine the number N2 of impulses thus transmitted per unitof time.

(3) Subtract the value N1 from the value N2, i. e. determine na:Iv'2N1.

It is apparent from the above that since N1 represents the number ofimpulses per unit of time that are larger than a-l-Aa and N2 representsthe number of impulses per unit of time that are larger than a the valueTLa=Nl-N2 represents the number of impulses per unit of time havingmagnitude comprised with the limits a and a-l-Aa.

In order to produce a representation of the spectral distribution of theincoming radiation, the following further instrumental steps arenecessary:

(4;) Vary continuously the characteristics of the channels A and B so asto scan with the value a a determined range from zero to as anddetermine the corresponding variation of m.

(5) Produce a trace representing visually the relationship between m and(1.

Consider now again Fig. 1. The voltage impulses derived from the outputterminals 59, 5| of the detector i2 are applied through an amplifier 52having output terminals 53, 54 to the channels A and B. Each channel ischaracterized by a threshold value and is arranged to transmit onlythose impulses the magnitude of which exceeds the correspondingthreshold value. Furthermore, the threshold values of the channels A andB are arranged to vary sinusoidally with respect to time. Let thethreshold value of the channel A vary with time as O.5as(+sin wt) +Aaand the threshold value of the channel B vary with time as 0.5a3(1+sinwt). Consequently, at any instant t the impulses transmitted through thechannel A are larger than 0.5a3 (1+sin wt) +Aa and the impulsestransmitted through the channel B are larger than O.5a3(1+sin wt).

The channels A and B connect the output terminals 53, 54 of theamplifier 52 to two frequency responsive networks 56, 57, respectively.In particular, the channel A connects the terminals 58, 5! to the inputterminals 58, 59 of the frequency responsive network 56 and the channelB connects the terminals 52, 5| to the input terminals iii), 6| of thefrequency responsive network 5?.

The channel A comprises a battery 62 in series with a rectifier 63 andresistor 64 interposed between the terminals 53, 53 and a source ofalterhating voltage 86 interposed between the terminals 54, 59 throughleads 61, 68. Let the voltage of the battery 62 be E1 and the voltage ofthe A. C. source 66 be E'z sin wt. These two voltages are arranged tooppose the voltage impulses derived from the terminals 53, '55 and theircombined value is equal It is apparent that in order to obtain thevoltage transmitted through channel A and applied to the outputterminals 58, 52 we should subtract from the voltage across the inputterminals 53, 54 the sum of the voltages of the A. C. source 6% and thebattery 62 and to rectify the obtained difference. Consequently, thechannel A has a threshold, and the value of this threshold is determinedby the sum of the voltages of the A. C. source 68 and the voltage of thebattery 62, i. e. it is equal to 0.5aa(1+sin wt) +Aa. Since the value ofthe A. C. source varies, this threshold Voltage is subjected tocontinual and-recurrent variations that is represented by the downwardand upward motion of the horizontal line in Fig. 2, the distance of saidhorizontal line from the axis of abscissa indicating at any instant thevalue of said threshold. Assume that at the instant under considerationt1 the threshold value 0.5a3(1+sin wt) +Aa=a1-+Aa. Then only theimpulses that are above said threshold value are applied to the outputterminals 58, 59, said impulses being 2, 4, 5, 8, 11, 14, 15, 18, 21,22, 25, 26, 27, 28, 30, 31, 32, and 33. These impulses are transmittedthrough the terminals 58, 59 to the frequency responsive network 56.

The channel B comprises a battery 8! in series with a rectifier BI and aresistor 82 interposed between the terminals 53, 6B and the alternatingvoltage source 66 interposed between the termiplied to the outputterminals till, El we should subtract from the voltage across the inputterminals 53, 54 the sum of the voltages of the A. C. source 66 and thebattery 80 and to rectify the obtained difference. Thus the channel Bhas also a threshold value that is determined by the sum of the voltagesof the A. C. source 65 and the voltage of the battery 80. The voltage ofthe battery 3% is smaller than the voltage of the battery 62 by anamount Aa and therefore the threshold of the channel B is represented atany instant by the value 6.5m; (1+sin wt). Since the value of the A. C.source varies the threshold voltageof'the channel B is also subjected tocontinual and recurrent variations that are represented by the downwardand upward motion of the horizontal line in 2, said line being alwaysbelow the line corresponding to channel A by the amount no. Since attheinstant t1 under consideration the instantaneous threshold value ofthe channel B is represented by the line a1 only the-impulses above thisline such as the ones designated in Fig. 2 by the. numerals 2, 3, 4, 5,6, 8,11, 13, l4, l5, l6, 17, 18, 21, 22, 24, 25, 26, 27, 28, 30, 31, 32,33 are transmitted through the channel B and applied to the frequencyresponsive network 51.

The frequency responsive networks 5%, 5? are of standard constructionand are adapted to produce across their output terminals 33, 83 and 90,9|, respective, D. C. voltages. The D. C. voltage derived from theoutput terminals 39 represents'the frequency of impulses applied to theinput terminals 58, 59 and the D. C. voltage derived from the outputterminals 80, 9! represents the frequency of the impulses applied to theterminals 6i), 6!.

The outputs of frequency responsive networks 55 and 57 are connected inopposition, i. e., the negative terminal 89 has the same polarity as thenegative terminal 9!. Consequently, the difference of voltage betweenthe terminals 88 and 9t applied to leads 92 represents-the frequency ofimpulses contained within two limiting values: 0.5m (l-l-sin wtH-Aa and0.5(13 (1+sin wt). At the instant h under consideration the voltagebetween the leads 92 represents the intensity of the flux of photons orparticles contained between the value al+Aa=O.5c (1+sin wti) +1112 andai -0.5m (l-l-sin wti). The voltage derived from leads is applied tovertically deflecting plates 93 of a cathode ray oscillograph 9 3and'defle'cts the electron beam by an amount representative of theintensity of photon or particle'fiux between the energy values art-Adiand a1.

Because of the varying voltage of the A. C. source 8d a scanning processtakes place which causes the voltage applied to plates 83 to vary inmagnitude and to represent at any instant the frequency of impulsescomprised within the value 0.5% (1+sin wt) +Ac and 0.5% (1+sin wt). Thisvoltage is applied to the vertically deflecting plates 93 of the cathoderay tube 94. Thus the luminous spot produced by the cathode ray beam isdeflected vertically by the amount representing the ordinate of thecurve of Fig. 3, i'. e., the intensitiesof the energy component scanned.

' The cathode ray tube 93 is provided with horizontally deflectingplates- 95, oneof said plates being grounded and the other plates beingconnected through lead 95 to the A. C. source 66 and then to ground.

. The voltage of the A. C. source 66 applied to the horizontallydeflecting electrodes 95 of the oathode ray tube 93 represents at anyinstant the threshold value applied to the channels A and B. Thisvoltage also represents energy ranges of individual photons orparticles. It is apparent that the voltage applied to the horizontallydeflecting plates at: of the cathode ray tube represents the values ofabscissa in the diagram of Fig. 3 since these values correspond toenergy or frequency ranges. On the other hand the voltage applied to thevertically deflecting plates 93 of the oathode ray tube represents atany time the number or particles per second, i. e., the intensity ofradiation within corresponding energy ranges. Consequently, in thediagrammatic representation of Fig. 3, the voltage applied to the plates93 represents the values of the ordinates since these values correspondto intensities of various radiation components. During the process ofscanning described above, these two voltages vary sunultaneously ther bycausing the spot produced by the cathode ray tube to produce a curvesuch as the one shown in Fig. 3 and representing the energy spectrum ofthe radiation impinging upon the detector i2.

Fig. it) shows another embodiment of the instrument for producingspectral distribution of heavy ionizing particles. A heavy particle suchas alpha particle, proton or a nucleus projected during thedisintegration process from a source ltd ionizes the gas between the twoconducting plates it 2, 52. A voltage V supplied by the battery I53drives the positive ions upon the collector I52 and hence upon the gridof the first tube I54 of the first amplifying stage I55; after which theions leak away to the ground. The output of the first amplifier I55 issubjected to further amplification in the linear amplifier I56. Thepulse is amplified in such a manner that the output across the terminalsI53, I58 is in direct proportion to the ionization produced in the shallow chamber between the electrodes 15!, I52 by each incoming particle.

For neutrons we may use in the chamber hydrogen at relatively highpressure or the walls of the chamber may be lined with parafiin, overwhich a light conducting coat of graphite is used. Various other formsofthe detector have been described in Electron and Nuclear Counters by$.Korfr", B. Van Nostrand 00., New York, N. Y., 1945 (see also ProposedNeutron Spectrometer in the 16-10300 Kev. Range by B. T. Feld, May 17,19%6, distributed by Office of the Publication Board, Dept. of Commerce,Washington, D. C.

Fig. 4 represents another embodiment of a. nuclear spectrometercomprising same three components as, the nuclear spectrometer of Fig. 1,namely the detector 12, an electrical transducer within the dotted linesIt and cathode ray tube indicator l'l. The detector and the cathode rayindicator areidentical in Fig. 1 and Fig. 4. They have been, therefore,designated by the same numerals. The electrical transducer it in Fig. 4is schematically different from the electrical transducer It in Fig. 1;it performs, however, the same function to translate the detector outputinto voltages to be applied to the cathode ray tube for representingvisually the spectral distribution of incoming photons or particles.

Consider now more in detail the electrical transducing network I6. Itcomprises an amplifier IIO connected to the detector I2 and having itsoutput applied to the input terminals III, II2 of a pulse shapingnetwork I I4.

The network II4 consists of a series arm comprising a rectifier H5 and ashunt arm comprising a condenser H6 in parallel with a resistance I IT.The type of impulse applied to the input of the network H4 is of shapeshown diagrammatically in Fig. 5a in form of a line ABD representing thevariation of the magnitude of the impulse with respect to time. Theimpulse is shown to appear at an instant OA, then rises in accordancewith a definite slope until an instant DC at which instant it attainsthe maximum value CB then it decays and at an instant OD reaches thevalue zero. Such a voltage impulse is effective to charge suddenly thecondenser I I6 and to cause the condenser to discharge through theresistance I I1. As a result of this we obtain across the outputterminals I29, I2I of the network II4 an impulse shown diagrammaticallyin Fig. 5b. The impulse is shown to appear at the instant OFapproximately coinciding with the instant AC, then it rises to itsmaximum value KG=CB and subsequently decays in accordance with the lineGH. Thus the pulse shaping network H4 receives at its input an impulsesuch as the one of Fig. 5a and produces across the output terminalscorresponding impulses shown in Fig. 5b rising to the same height as theinput impulse but having a longer time of decay.

The impulses derived from the network H4 are then simultaneously appliedto two channels A1 and B1. Each channel is characterized by a thresholdvalue that varies cyclically with respect to time and is arranged totransmit those impulses the magnitude of which exceeds the thresholdvalue. The channel A1 has a threshold value 0.5a3(l+sin wt)+Aa whilechannel Bl has a threshold value 0.5a3(1+sin wt) where Aa is arelatively small magnitude.

The channel A has input terminals I20, I 2I and output terminals I22,I23. The input terminal I is connected through the resistor I24 to thegrid I25 of a triode I26, said triode having its cathode I21 connectedin series with a biasing battery I20 and a source of alternating voltageI29. The voltage source I29 and the input terminal I2I are grounded. Theplate I30 of the triode I26 is connected through the output terminalI22, resistor I3I to the output terminal I 23 and then through thebattery I32 to ground.

The channel B has input terminals I20, I2I and output terminals I23,I36. The input terminal I20 is connected through the resistor I3'I tothe grid I36 of a triode I39, said triode having its cathode I40connected in series with a biasing battery MI and a source ofalternating voltage I29. The plate I42 of the triode I39 is connectedthrough the output terminal I36, and the resistor I44 to the outputterminal I23 and then through the battery I 32 to ground.

, Itis apparent that we obtain across the output terminals I22, I23 onlythose impulses that are capable of overcoming the biasing voltage of thetube I26. Assume that the voltage of the battery I26 is E 1 and thevoltage of the A. C. source I29 is E 2 sin wt and that the total biasingvoltage E 1+E 2 sin wt=0.5a3 (1+sin wt) +Aa. It is apparent thereforethat only the voltage impulses that are capable of exceeding thethreshold value 0.5a: (1+sin wt) +Aa are trans- 8. mitted through thechannel A1 and appear across the output terminals I22, I23.

Similarly in the channel B only those voltages appear across the outputterminals I36, I23 that are capable of overcoming the biasing voltage ofthe tube I39. Assume that the voltage of the battery MI is E 3=E 1Aa.Then the total biasing voltage of the tube I39 is E 3+E 2 sin wt=0.5as(1+sin wt). Consequently, only the impulses that are capable ofexceeding the threshold value 0.5a3 (1+sin wt) appear across theterminals I36, I23.

It is apparent that the two output voltages across the terminals I22,I23 and I36, I23 are mounted in opposition, so that the resultant outputbetween the'terminals I22, I36 is equal to their difierence. Considernow three cases des ignated as (a) (b) (c). Case (a).-The impulsederived from the terminals I20, I2I has a value below the thresholdvoltage of the tubes I26 and I39. Consequently, no plate currents wil1be delivered by these tubes and no voltage will appear across theterminals Case (b).The impulse derived from the terminals I20, I2I has avalue above the threshold voltage of the tubes I26 and I39.Consequently, both tubes deliver plate currents, and two short voltageimpulses appear simultaneously across the output terminals I22, I 23 andI36, I23. Since these two voltages are equal one to another, theresultant voltage across th terminals I22, I36

is zero.

Case (c).The impulse derived from the terminals I20, I2I has a valuelarger than the threshold of the tube I39, i. e. larger than 0.5m (1+sinwt) and smaller than the threshold of the tube I26, i. e. smaller than0.5013 (1+sin wt) +Aa Consequently, a plate current will pass throughthe tube I39 and no plate current will pass through the tube I26.Consequently, no voltage wil1 be produced across the terminals I22, I23and a short voltage impulse will appear across the terminals I36, I23.We obtain, therefore, across the terminals I36, I22 a resultant voltagecoincident with the impulse derived from the terminals I20, I2I.

It is therefore apparent that at any instant t only those impulses thatare comprised within the energy range limited by values 0.5113 (1+sinwt) and 0.5a: (1+sin wt) +Aa produce corresponding output impulsesacross the terminals I36, I22. These output impulses are in turn appliedto a resistor I 50 in series with a condenser I5I and in series with aresistor I52. We therefore obtain across the output terminals I53, I54 avoltage that is substantially equal to the number of impulses per secondcomprised within the energy range limited by values 0.5123 (1+sin wt)and 05m (1+sin wt) +Aa This voltage is in turn applied to the verticallydeflecting plates 93 of the cathode ray tube 94.

Because of the varying voltage of the source I29 as the scanning processtakes place; the voltage applied to the plates 93 varies in magnitude soas to represent at any instant the frequency of impulses comprisedwithin the values 0.5m (1+sin wt) +Aa and 0.5a3(1+sin wt) The cathoderay tube 93 is provided with horizontally deflecting plates 95, one saidplate being grounded and the other plate being connected through leadI10 to the A. C. source I23 and to ground.

Consequently, the voltage of the A. C. source I29 applied to thehorizontally deflecting plates '95 of the cathode ray tube 93 representsat any instant the threshold value applied to the channels A and 3?.This voltage also represents energy ranges of individual. photons orparticles. Thus, the Voltage applied to the horizontally deflectingplates 95 of the cathode ray tube is represented by the values ofabscissa in the diagram of Fig. 3 since said values correspond to energyand frequency ranges. On the other hand, the voltage applied to thevertically defleeting plates 93 of the cathode ray tube t l representsat any time the number of photons or particles per second, i. e. theintensity of radiation within said energy ranges. This corresponds tothe values of trdinates in Fig. 3 since these values represent theintensities of various radiation components.

During the process of scanning described above, these two voltages varysimultaneously thereby causing the spot produced by the oathnde ray tubeto move along a curve such as the one shown in Fig. 3 representing theenergy spectrum of radiation impinging upon the detector I2.

Fig. 6 represents another embodiment of a nuclear spectrometercomprising the same three components as the nuclear spectrometer of 1,namely, the detector it, an electrical transducer within the dottedlines I6 and a cathode ray tube indicator within the dotted lines I!.The detector I2 and the cathode ray tube indicator ii are identical inFig. l and 6. They nave, therefore, been designated by the samenumorals. The electrica1 transducer H6 in Fig. (3 is schematicallydifferent from the electrical transducer I5 in Fig. 1. It performs,however, the same function to translate the detector output intovoltages to be applied to the cathode ray tube for representing visuallythe spectral distribution of incoming photons or particles.

Consider now more in detail the electrical transducing network it. Itcomprises a varying threshold channel connecting the output terminals2M, Zlll of the detector I2 to the input terminals 252, 2513 of afrequency responsive net'- work 204. In particular the varying thresholdchannel comprises a battery 295 in series with a rectifier 205 and aresistor 28'! interposed between the terminals 259, 2&2 and a voltagesource 2 I [I interposed between the terminals 2i! i, 293. The source 2Mis of a typ well known in the art adapted to generate a saw toothvoltage varying recurrently from a value (a3/ 2) to the value +(as/2) inaccordance with the diagram shown in 6a. Let the voltage of the battery205 be equal to (as/2). The battery voltage and the voltage of thesource 2 it! are arranged to 0p pose the voltage impulses derived fromthe t-ermi-- nals 2%, 2!) I. Let the instantaneous value of the sum ofthe two voltages be 0,05), where mt) is sawtooth wave varyingrecurrently and linearly from zero to the maximum value as. At eachinstant t there is a number no) of impulses that exceed theinstantaneous threshold Value a(t). In this particular case we areinterested in the number of impulses m, which are contained within anarrow range having limits at and a-l-Aa. Assume that at an instant(t-l-at) the instantaneous threshold value becomes c-l-nc and thecorresponding number of impulses eX- iii;

ceeding the new threshold value becomes N-l-AN. Itis apparent thatNa=(AN/At)=(dN/da) (1) Since the function a(t) has a sawtooth form, i.e. increases linearly with respect to time, We can write Ne: (dN/da)=K(dN/dt) where K is a suitable constant.

Referring now again to Fig. 6 it is seen that at any instant t, N(t)impulses are applied to the input terminals of the frequency responsivenetwork 2534. We obtain thus across the output terminals 23 l, 2I2 ofthe network 204 a unidirectional voltage having magnitude proportionalto NU). This voltage is in turn applied to a derivator circuit containedwithin the block 2M. The derivator circuit is adapted to perform theprocess of derivation ele trically in such a manner that when itreceives between its input terminals 2H and 2H2 a certain voltage itdelivers across its output terminals 255 and ZIB another voltage varyingsubstantially as the derivative with respect to time of the inputvoltage. The derivator 2M consists of a capacitor 2I'I inserted betweenthe terminals 2 and 2I5 and of the resistor 258 inserted between theterminals H5 and 216.

It is thus apparent that we obtain across the output terminals 255, 2! 6of the circuit 2M a voltage proportional to (dN/dt). It is also apfromthe formula given above that this voltage represents the number 71a ofphotons comprised at the given instant within a very narrow range(having a width Aa) above the threshold value mt). This voltage isapplied after suitable amplification by means of the amplifier tie tothe vertically deflecting plates 93 of the cathode ray oscillograph S4.The horizontally deflecting plates 95 of the oscillograph are connectedby means of loads 22!! to the sawtooth wave generator 2w. The circuit isprovided with conventional blackout arrangement during the beginning ofeach sawtooth cycle.

It is apparent that we obtain on the screen of the cathode ray tube adiagram representing the spectrum of incoming radiation, substantiallysimilar to the one shown in Fig. 8.

Consider now the derivator 2M. Its operation can be explainedmathematically as follows:

Let Brut) be the function representing the voltage applied across theinput terminals 2H and 2I2 of the derivator 214, Bad) the functionrepresenting the voltage across the output terminals 2 i5 2 I6, C thecapacitance of the capacitor 2 I l, R the resistance of the resistor 2 I3 and Hi) the current flowing through the capacitance 2H. Assume alsothat the output terminals and ZIG of the derivator 2M have beendisconnected from the amplifier 2I9. Consequently, the same current2'(t) flows through the capacitance 2!! and through the resistance 2!?and the following relation holds true:

a o= t odl+Rv o 3) Differentiating this equation we obtain:

selecting the proper values of the resistance for example, making Rnegligibly small, the term R di/clt can be made negligible as comparedto Hi) /C and the following relation may 11 held" withan approximationsatisfactory for practical purposes:

dB (t) 1 Multiplying both sides of the equation by C R we obtain:

Consequently, the expression R iflf) which represents the voltage dropacross the resistor 2l8 between the output terminals 2|5 and 216 issubstantially proportional to dB1(t) /dt.

The arrangement is illustrated in Fig. 1 and Fig. 4 is particularlyadapted to provide energy distribution of relatively strong radiation inwhich the time interval for determining the number of counts need not tobe excessively long in order to render the random fluctuationsnegligible. If, however, the time interval necessary for a satisfactorymeasurement is large it is desirable to use a measuring arrangement asillustrated in Fig. 7a, 7b. The arrangement shown in these figurescomprises two components: a recorder illustrated in Fig. 7a and areproducer illustrated The recorder comprises a portion of the elementsof Fig. 1 or Fig. i such as a detector l2 exposed to a radiation source239. The source 239 may emit any radiations resulting from nucleardisintegrations such as alpha rays, gamma rays, photons, neutrons, etc.The detector I2 is of an appropriate form depending upon the type ofradiation that it is desired to detect. spond to either of saidradiations and to produce across the output terminals 23! voltageimpulses coincident with incoming photons or particles and havingmagnitudes representing the energies of said individual photons orparticles. The output terminals 23! are applied to a recording head 232of suitable magnetic recorder 233. The recording head 232 is inoperative relation to a magnetic tape 234 that runs upward in thedirection indicated by the arrow. Two spools or reels 235, 235 serve assupport for the tape and are arranged to be driven by a motor 237.

The recording head 232 consists of an electromagnet having an iron coreand a winding wound around the core. The core is provided with two polepieces immediately adjacent one to another. The pole pieces are providedwith sharp edges in form of knife blades in order to localize within anarrow zone of exploration the flux that passes between them. The narrowair gap between the pole pieces is designated by 238. The tape 234 ismade to pass through the air gap in such a manner, that the plane of thetape is perpendicular to the line joining the pole pieces and the tapeis assumed to be wound upon the spool 236 and the motion of the tape inthe direction indicated by the arrow is produced by unwinding the tapefrom the spool 236 and winding it upon the spool 235.

The electrical impulses derived from the detector l2 after a suitableamplification in the amplifier 239 induce corresponding impulses ofmagnetic field within the recording head 232, the magnitude of saidimpulses representing energies of corresponding photons or particles.Therefore, as the tape 23% is moved in the direction of the arrow asdescribed above, it is brought to a very high transverse magnetizationby the flux impulse set up in the pole pieces of therecording head Bytransverse magnetization it is meant that Consequently, the detector l2may re the flux in the tape'is in the direction of its thick ness. It isalso .apparent that after this portion of the tape has left the air gapand proceeds in the direction of'the arrow towards the spool 235, asubsequent portion of the tape enters the air gap and becomessubsequently magnetized in the direction perpendicular to the tape, andto the extent dependent upon the strength of the succeeding magneticfield impulse in the air gap at said subsequent instant. Because of themagnetic retentivity, each element of the tape, after having passedthrough the air gap, acquires a magnetic moment which is oriented in thedirection perpendicular to the tape.

It is therefore apparent that the tape 234, during its motion in thedirection of the arrow becomes wound upon the spool 235, and retains asuccession of magnetic moments, the distribution of which with respectto the length of the tape has a relationship to the individual energiesand to the time succession of photons or particles traversing thedetector I2.

Fig. 7b shows the reproducing components for translating the recordingsmade upon the magnetic tape 23 1 into an energy spectrum upon the screenof a cathode ray oscillograph similar to the one described above. Thearrangement shown shows a magnetic reproducer. The out: put of themagnetic reproducer after a suitable amplification is applied to atransducer l6 and then to a cathode ray tube indicator ll. Transducer l6and the cathode ray tube indicator ii are identical. in Figures 7a, b,and Fig. 1. Therefore, similar elements are designated by the samenumerals in Figs. 7a, b, and Fig. 1.

The magnetic reproducer comprises the usual reproducing head 242associated with the tape 234 at a point between the two spools 243, 244.In order to reproduce the energy impulses of income ing photons orparticles impressed magnetically upon the tape 235i, the tape has to bemoved linearly through the reproducing head 242 in the directionindicated by the arrow. At the initial instant, the magnetized tapecontaining the record of the impulses is completely wound upon the spool223, the impressions being reproduced by progressively unwinding thespool 223, whereby the tape 23! is made to move past the reproducinghead 2 52 and becomes progressively wound upon the spool 244. Asshown inthe figure, the unwinding of the spool 2G3 and the simultaneous windingof the spool 244 is efiected by means of a motor 245.

The reproducer head 262 is structurally similar to the recording head232. In particular, the reproducer head consists of an electromagnethaving an iron core and a winding wound around the core. The core isprovided with two pole pieces having a form of two relatively sharpedges and immediately adjacent one to another. The narrow air gapbetween the pole pieces is designated by 245. The tape 234 is made topass through the air gap 246 in such a manner that the plane of the tapeis perpendicular to the line joining the po e pieces.

It is apparent that the successive portionscf the tape containing themagnetic impressions of the energy impulses pass through the air gap255. In the manner shown, the pole pieces will each supply a convenientmagnetic path for the chang ing flux resulting from the passage of themagnetized tape and cause this flux to pass through the associated coil.This changing flux generates a voltage in the coil. We therefore obtainacross the output terminals 259 of the reproducing head a succession ofvoltage impulses such as shown in Fig. 2, i. e. similar to the voltageimpulses that appeared across the output terminals of the detector i2.

The operation of the arrangement of Fig. 7a. b is based therefore uponproducing a magnetic record on a suitable tape 23 of the output of thedetector l2 and subsequently reproducing the record, thereby derivingthe impulses representing the detector output. Using instrumental stepssimilar to those in Fig. 1 the electric impulses derived from themagnetic reproduccr are simultaneously transmitted to channels No. I andNo. 2 differing one from the other by their threshold value. Byproviding a suitable scanning with said threshold valves and with themeans of the cathode ray tube a graph is produced upon the screen of thetube that represents the energy distribution of the radiations impingingupon the detector. The manner according to which the impulses derivedfrom the magnetic reproducer are utilized to produce the energydistribution in the cathode ray oscillograph has been described inconnection with Fig. 1.

In the illustration chosen for 7b the block l5 translating the output ofthe reproducer into suitable voltages to be applied to the cathode raytube 93 is of the same type as block IS in Fig. 1. It is, however,apparent that we may use in 7b the arrangement represented by block. itin Fig. 4 for the purpose of translating the reproduced impulses intosuitable voltages to be applied to the cathode ray tube.

The magnetic recording tape 234 shown in Fig. 7a and Fig. 71) forms aclosed loop having a certain length L cm. Let the lineal speed of thetape during the recording process be V1 c1n./ sec. Consequently, thetime interval corresponding to one complete revolution of the loop 234during the recording is T1==(L/V1) second ('7) Assume that the linealspeed of the magnetic tape during the reproducing be V2 cur/sec.Consequently, the time interval corresponding to one complete revolutionof the loop during the reproducing is T2=(L/Vz) second (8) Two methodsshall be considered. In the first one Vz==nV1 (9) i. e. the lineal speedV2 during the reproduction is n times larger than the lineal speedduring the recording. Furthermore, the recording is effected only onceduring T1 seconds, i. e. during one complete revolution of the loop 234while the reproducing is effected continually and recurrently with theperiod of T2 seconds.

It is apparent that in accordance with this method the number ofrevolutions per minute of the motor 245 is n times larger than thenumber of revolutions of motor 237. Consequently, the rate at which thecurrent impulses are applied to the transducer Hiin Fig. 7b are n timeslarger than the rate at which the corresponding energy quanta impingeupon the detector I2 from the source 230. It is apparent therefore thatthe frequency of impulses in the portion of the instruments of Fig. 7bare n times larger than the frequency of. corresponding energy quanta.

Consequently, the impulses applied to the input terminals 258 of theblock iii in Fig. 7b are identical to impulses that would have beenobtained from a source n times stronger directly without the use ofmagnetic recorder-reproducer (by means of the arrangement of Fig. 1 orFig. 4).

Therefore, in order to obtain the spectral distribution of photons orparticles from a weak source two steps are necessary. The first stepconsists in recording the incoming particles or photons on a suitabletape running at relatively low speed and we may limit the recording timeto one complete cycle of the loop 234. The second step consists inreproducing the tape impression while running the tape at a speed 11times greater, thus producing results that would have been obtaineddirectly from a source of radiations n times stronger.

The second method differs from the first in that the recording time isequal to T1 =nT1=n (L/V1) second (10) i. e. the recording time is ntimes larger than one period of revolution of the loop 2 34. It isapparent that during each period T1 the loop receives a succession ofmagnetic impressions that distribute themselves throughout its length inaccordance with the time distributions of photons or particles radiatedfrom the source 230. It is noted that the complete recording timecomprises n such periods and each period brings its own contribution ofmagnetic impressions that distribute themselves upcn the tape and add toimpressions made during the preceding periods. Consequently, the numberof impulses impressed upon the tape 234 after the completion of 12.periods is n times larger than the number of impulses obtained duringone period. Consequently, the magnetic impressions obtained on the tape234 are the same if the source were n times stronger and the recordingprocess were limited one to one period of revolution of the turn. Inorder to reproduce the signals from the tape 234 it is desirable to runthe tape at a speed V2 that is greater than V1 although in this methodit is not essential since the disadvantages of using a weak source 230have been overcome by increasing the recording time n times.

We may synthesize the above consideration as follows: Let N1 representthe number of complete revolutions of the tape 233 during the recordingprocess and R1 the number of impulses per second derived from thedetector I2. It is apparent that the number D of magnetic impressionsper unit of length of the tape 233 will increase proportionately to R1and N1 and will decrease proportionately to the linear speed V1 cm./sec.of the tape, i. e.

It is also apparent that the number of im-. pulses reproduced per secondfrom the magnetic tape is proportional to the number D of magneticimpressions per unit of length and to the lineal speed V2 cm./sec. ofthe tape during the reproduction, i. e.

NIVZ 1 For the satisfactory operation of the instrument it is necessaryfor R2 to be larger than R1, i. e. the number of impulses per sec.during reproduction should be larger than during recording; consequentlyand the speed V2 should be larger than Fig; 'ZCilIustrates' aimodified'embodiment of the invention in which instead of a closed loop 23 we useas a carriervof magnetic impressions atape llllgthe length of which isvery great as compared to the value of L cm. The tape is being unwoundfrom the spools 59! to the spool'502 by means of an appropriate motor563 driving the spool 502 clockwise. The tape moves in the direction ofthe arrow and passes in proximity of a recording head 503, reproducinghead 50 iand erasing head 5% suitably displaced one from another. Theerasing head is connected to an A; C. source 507.

The portion ofv the wire between the points -A and B containsimpressions of magnetic impulses obtained by means of an arrangementsimilar to the one of Fig;' 7a and representing the succes sion ofphotons or particles detected by means of the detector 12 and recordedduring a suitable time interval T1:(L/V1) sec.

During the reproducing process we obtain across the output terminals515) of the reproducing head 504 a succession of impulses which are inturn applied to the transducing network i6 and to the cathode rayindicator i'i in the manner hereinabove' described. The reproducedimpulses de rived from the terminals Eli] are also amplified in anamplifier 5H and impressed upon the recording head 593 positioned at adistance L from the reproducing head 5%. Consequently, the signalsreproduced from the tape 50% by means oflhead 504 are simultaneouslyimpressed upon the tape by means of the head 593. The erasing head 505has as a purpose of erasing the magnetic impression'after they havepassed through the head 5%.

Consequently, three processes take place simultaneously during themotion of' the wire 569. These processes are as follows:-'

H (a) erasing of all the magnetic signals that have passed through thereproducing head 5136; Consequently, the portion of the moving tape-tothe right of the point A is being continually demagnetized.

-'(b) reproducing of all the signals that pass through thereproducinghead 5%. These signals transmitted through block it produce a visualindicationin the indicator l'l. Y

(-c) impressing upon the moving wire at the point B of all the signalsthat are being reproduced. 1

Consequently, the magnetic signals are being simultaneously erased-totheright of the point A and reimpressed at the paint B. Therefore, the

succession of magnetic impulses is continually r and recurrentlyreimpressed upon theportion of moving tape contained within the points Aand B. Accordingly, we obtain inthe output of the re producer head arecurrent succession of magnetic impulses producing the'same result asif a closed loop of the length L passed continually and recurrentlythrough the reproducing head 5%. Because of the retentivity of thecathode ray screen in the indicator li these recurrent impulses producea presistent visual indication representing the spectral distribution ofthe impulses recorded upon the tape 5%.

I claim:

1. Method of analyzingradiation consisting of individual photons or-,part icles succeeding each other, said photons or particles havingdifierent energy values, comprising the step of producing electricalimpulses coincident with said photons or particles and having magnitudesrepresenting the respective energies of said photons or par ".136ticles, selectively receiving a portion of said im-g pulses within adetermined, range oi-magnitudes and producing a signal representing saidreceived portion, varying said range and simultaneously producing anindication representing the relationship between said signal and saidrange.

2. Method of analyzing radiation consisting of individual photons orparticles succeeding each other, said photons or particles havingdifie'rent energy values, comprising the step of producing electricalimpulses coincident with said photons or particles and having magnitudesrepresenting the respective energies of said photons or particles,selectively receiving a portion of said impulses within a predeterminedrange of magnitudes, producing a signal representing the number ofimpulses within said range per unit of time, varying said range andproducing an indication representing the functional relationship betweensaid number of impulses and said range.

3. In an instrument for analyzing radiation consisting of individualphotons or particles succeeding each other, said photons or particleshaving difierent energy values, a detector responsive to said radiationfor producing a succession of impulses coincident with said photons orparticles and having magnitude representing the respective energies ofsaid photons or particles, a chan nel connected to said detector andhaving variable threshold for transmitting impulses exceed ing saidthreshold, a control element for varying the value of said threshold,and an indicator responsive to the output of said channel and operatedin accordance With the variation of said threshold for providing anindication of said radiation. i

4. Ina method of analyzing weak radiations, said radiations consistingof individual particles or photons succeeding each other at a rate thatis relatively low, the step of-- producing individual current impulsescoincident with said particles or photons, recording said impulses asthey-sue ceed each other upon a suitable tape and simultaneously movingsaid tape at a relatively low speed, the step of reproducing saidimpulses from said tape and simultaneously moving said tape at ahigherspeed, whereby said reproduced impulses succeed each other at arate correspondingly higher than the rate of said impressed irripulsesand the step of analyzing said reproduced impu1ses.-

5. In a method of analyzing weak radiations consisting of individualparticles or photons sucseeding each other at a rate that isrelativelylow, said particles or-photons having different energy values, the stepof producing individual current impulses coincident with said particlesor photons and having magnitudes representing the respective energies ofsaid particles or photons, recording said impulses as they succeed eachother upon a suitable tape and simultaneously moving said tape at arelatively low speed, the step of reproducing said impulses iromsaidtape and simultaneously moving said tape at a higher speed, whereby saidreproduced impulses succeed each other at a rate correspondingly higherthan the rate of said impressed impulses, selec-' tively receiving aportion of said reproduced im pulses withina determined range ofmagnitude, producing a signal representing the rate of succession ofsaid reproduced impulses within said range, varying said range, andrepresenting a functional relationship between said signal and saidrange.

6.. In an instrument for analyzing-radiation consisting of individualphotons or particles succeeding each other, said photons or particleshave difierent energy values, a detector responsive to said radiationfor producing a succession of impulses coincident with said photons orparticles and having magnitudes representing the respective energies ofsaid photons or particles, a channel connected to said detector andmeans for transmitting impulses within a range of magnitudes, means forvarying said range, and an indicator responsive to said impulses andoperated in accordance with the variations in said range for providingan indication of said radiation.

'7. In an instrument for analyzing radiation consisting of individualphotons or particles succeeding each other, said photons or particleshaving different energy values, a detector responsive to said radiationfor producing a succession of impulses coincident with said photons orparticles and having magnitudes representing the respective energies ofsaid photons or particles, a movable signal carrier, means for drivingsaid carrier at a certain rate of speed, a recording element connectedto said detector for recording said impulses on said carrier while saidcarrier is driven at a certain rate of speed, means for changing to anew rate of speed at which said carrier is driven, reproducer elementfor reproducing said recorded impulses while said carrier is driven pastsaid element at said new rate of speed, a channel connected to saidreproducer and having a variable parameter for transmitting reproducedimpulses within a range of magnitudes determined by said parameter, acontrol element for varying the value of said parameter, and anindicator responsive to the output of said channel, and operated inaccordance with the variation of said parameter for providing anindication of said radiation.

8. In an instrument for measuring radiation consisting of individualphotons or particles succeeding each other at a rate that is relativelylow, a detector responsive to said radiation for producing a successionof impulses coincident with said photons or particles, a movable signalcarrier, means for moving said carrier at a certain rate of speed, arecording element connected to said detector for recording said impulseson said carrier while said carrier is driven at said certain rate ofspeed, means for changing the speed at which said carrier is moved,reproducer element for reproducing said recorded impulses while saidcarrier is moved past said reproduced element at said changed speed,whereby the reproduced impulses succeed each other at a rate that isrelatively high, and a measuring means connected to said reproducerelement.

9. In an instrument for measuring radiation consisting of individualphotons or particles succeeding each other at a rate that is relativelylow, a detector responsive to said radiation for producing a successionof impulses coincident with said photons or particles, an endlessmovable signal carrier, a recording element connected to said detectorfor impressing said impulses on said signal carrier, means for movingsaid carrier at a certain speed during a time interval sufiicient toeffect a determined numberof cycles in the motion of said carrier, meansfor imparting to said carrier a suitable speed, a reproducer element forreproducing said recorded impulses while said carrier is driven pastsaid reproducer element at said suitable speed, said suitable speedbeing determined in such a 18 manner that the rate of reproducedimpulses is larger than the rate of incoming impulses, and a measuringelement connected to said reproducer element.

10. In an instrument for measuring radiation consisting of individualphotons or particles succeeding each other at a rate that is relativelylow, a detector responsive to said radiation for producing a successionof impulses coincident with said photons or particles, a signal storageelement for receiving and storing said impulses and subsequentlyreproducing said impulses at a higher rate, and a measuring meansconnected to said element.

11. In an instrument for analyzing radiation consisting of individualphotons or particles succeeding each other at a rate that is relativelylow, said photons or particles having different energy values, adetector responsive to said radiation for producing a succession ofimpulses coincident with said photons or particles and having magitudesrepresenting the respective energies of said photons or particles, asignal storge element for receiving and storing said impulses andsubsequently reproducing said impulses at a higher rate, a channelconnected to said signal storage element and having a variable parameterfor transmitting reproduced impulses within a range of magnitudesdetermined by said parameter, a control element for varying the value ofsaid parameter, and an indicator responsive to the output or saidchannel and operated in accordance with the variation of said parameterfor providing an indication of said radiation.

12. In an instrument for analyzing radiation consisting of individualphotons or particles succeeding each other, said photons or particleshaving different energy values, a detector responsive to said radiationfor producing a suscession of impulses coincident with said photons orparticles and having magnitudes representing the respective energies ofsaid photons or particles, means responsive to said impulses forproducing simultaneously two electrical signals, one of said signalsrepresenting a selected range of magnitudes and the other signalrepresenting the number of impulses within said range, and meansresponsive to said signals for producing an indication representing arelationship therebetween.

13. In an instrument for measuring radiation consisting of individualphotons or particles succeeding each other, said photons or particleshaving different energy values, a detector responsive to said radiationfor producing a succession of impulses coincident with said photons orparticles and having magnitudes representing the respective energies ofsaid photons or particles, a selective network of variable selectivityadapted to transmit a portion of said impulses Within a range ofmagnitudes determined by said selectivity, and a scanning meansresponsive to the output of said network for continually and repeatedlyscanning the selectivity and for producing an indication showing arelations hip between the ouput of said network and said selectivity.

14. In an instrument for analyzing radiation consisting of individualphotons or particles succeeding each other, said photons or particleshaving different energy values, a detector r sponsive to said radiationfor producing a succession of impulses coincident with said photons orparticles and having magnitudes representin the respective energies ofsaid photons or pal ticles, a selective network connected to saiddetector for selectively transmitting a portion of said umpulses withina range of magnitudes determined by the selectivity of said network, andan indicator operated in conjunction with said selective network andresponsive to the output of said network for indicating the relationshipbetween said output and said selectivity.

15. In an instrument for measuring radiation consisting of individualphotons or parti les succeeding each other at a rate that is relativelylow, said photons or particles having different energy values, adetector responsive to said radiation for producing a succession ofimpulses coincident with said photons or particles and having magnitudesrepresenting the respective energies of said photons or particles, asignal storage element for receiving and storing said impulses andsubsequently reproducing said impulses at a higher rate, a selectivenetwork of variable selectivity adapted to transmit a portion of saidreproduced impulses within a range of magnitudes determined by saidselectivity, and a scanning means responsive to the output of saidnetwork for continually and repeatedly scanning the selectivity and forproducing an indication showing the relationship between the output ofsaid network and said selectivity.

16. In an instrument for measuring radiation consisting of photons orparticles succeeding each other and having different energy values, adetector responsive to said radiation for producing a succession ofimpulses coincident with said photons or particles and having magnitudesrepresenting the respective energies of said photons or particles, amovable carrie means for driving said carrier at a certain rate ofspeed, a recording element connected to said detector for recording saidimpulses on said carrier while said carrier is driven at a certain rateof speed, u

means for changing to a new rate of speed at which said carrier isdriven, reproducer element for reproducing said recorded impulses whilesaid carrier is driven past said element at said new rate of speed, aselective network of variable selectivity connected to said reproducerelement for transmitting a portion of reproduced impulses within a rangeof magnitudes determined by said selectivity, another network connectedto said selective network for producing a signal representing the rateof occurrence of said transmitted impulses, and a scanning meansresponsive to the output of said other network for varying thselectivity of said first network and for producing an indicationshowing relationship between said signal and said selectivity.

1'7. Apparatus for determining the composition of an unknown substance,comprising a source of neutrons for bombarding a sample of saidsubstance with a stream of neutrons to produce the radiation ofparticles or photons from said substance ha ving energies related to thecharacter of the elements in the substance and in numbers related to therelative amounts of said elements in said substance, means forconverting said particles or photons into electrical signals havingamplitudes representing the respective corresponding energies of saidparticles or photons, means for measuring the number of said signalshaving amplitudes within a predetermined range, and means for shiftingthe amplitude range within which said signals ar measured withoutsubstantially changing the width of said amplitude range.

JACOB NEUFELD.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,289,926 Neufeld July 14, 1942 2,296,176 Neufeld Sept. 15,1942 2,303,688 Fearon Dec. 1, 1942 2,331,189 Hipple Oct. 5, 19432,337,306 Barnes Dec. 21, 1943 2,378,389 Begun Jan. 19, 1945 2,424,218Begun July 22, 1947 2,469,460 Fearon May 10, 1. 749 2,508,772 PontecorvoMay 23, 1950 OTHER REFERENCES The Interval Selector, RobertsR.ev. ofSci. Instruments, February 1941, vol 12, pp. 71-76.

Roberts--Review of Scientific Instruments, January 1940, pp. 44-45, vol.11.

KorffElectron and Nuclear Counters, D. Van Nostrand, Inc., New York,April 1946, pp. 196-197, pp. 18, 19.

